Stent with dual support structure

ABSTRACT

A intraluminal stent comprises a reticulated tube having an un-deployed diameter and expandable to an enlarged diameter. The tube includes a structural beam extending between first and second ends. The structural beam changes from a first geometry to a second geometry when the tube changes from the un-deployed diameter to the enlarged diameter. The structural beam includes first and second longitudinal elements each extending at least partially between the first and second ends and with a spacing between the first and second elements. Each of said first and second elements changes from the first geometry to the second geometry when the tube changes from the un-deployed diameter to the enlarged diameter for the spacing to remain substantially unchanged as the tube changes from the un-deployed diameter to the enlarged diameter.

I. CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of copending andcommonly assigned U.S. patent application Ser. No. 09/049,486 filed Mar.27, 1998, entitled “STENT” and naming Paul J. Thompson as sole inventor.

II. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to stents for use in intraluminal applications.More particularly, this invention pertains to a novel structure for suchstents.

2. Description of the Prior Art

Stents are widely used for numerous applications where the stent isplaced in the lumen of a patient and expanded. Such stents may be usedin coronary or other vasculature, as well as other body lumens.

Commonly, stents are cylindrical members. The stents expand from reduceddiameters to enlarged diameters. Frequently, such stents are placed on aballoon catheter with the stent in the reduced-diameter state. Soplaced, the stent is advanced on the catheter to a placement site. Atthe site, the balloon is inflated to expand the stent to the enlargeddiameter. The balloon is deflated and removed, leaving the enlargeddiameter stent in place. So used, such stents are used to expandoccluded sites within a patient's vasculature or other lumen.

Examples of prior art stents are numerous. For example, U.S. Pat. No.5,449,373 to Pinchasik et al. teaches a stent with at least two rigidsegments joined by a flexible connector. U.S. Pat. No. 5,695,516 toFischell teaches a stent with a cell having a butterfly shape when thestent is in a reduced-diameter state. Upon expansion of the stent, thecell assumes a hexagonal shape.

In stent design, it is desirable for the stent to be flexible along itslongitudinal axis to permit passage of the stent through arcuatesegments of a patient's vasculature or other body lumen. Preferably, thestent will have at most minimal longitudinal shrinkage when expanded andwill resist compressive forces once expanded.

III. SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, anintraluminal stent is disclosed. The stent comprises a reticulated tubehaving an un-deployed diameter and expandable to an enlarged diameter.The tube includes a structural beam extending between first and secondends. The structural beam changes from a first geometry to a secondgeometry when the tube changes from the un-deployed diameter to theenlarged diameter. The structural beam includes first and secondlongitudinal elements each extending at least partially between thefirst and second ends and with a spacing between the first and secondelements. Each of said first and second elements changes from the firstgeometry to the second geometry when the tube changes from theun-deployed diameter to the enlarged diameter for the spacing to remainsubstantially unchanged as the tube changes from the un-deployeddiameter to the enlarged diameter.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a stent accordingto the present invention shown in a rest diameter state and showing aplurality of stent cells each having a major axis perpendicular to anaxis of the stent;

FIG. 2 is a plan view of the stent of FIG. 1 as it would appear if itwere longitudinally split and laid out flat;

FIG. 3 is the view of FIG. 2 following expansion of the stent to anenlarged diameter;

FIG. 4 is a view taken along line 4-4 in FIG. 2;

FIG. 5 is a view taken along line 5-5 in FIG. 2;

FIG. 6 is an enlarged view of a portion of FIG. 2 illustrating a cellstructure with material of the stent surrounding adjacent cells shown inphantom lines;

FIG. 7 is the view of FIG. 2 showing an alternative embodiment of thepresent invention with a cell having five peaks per longitudinalsegment;

FIG. 8 is the view of FIG. 2 showing an alternative embodiment of thepresent invention with a major axis of the cell being parallel to anaxis of the stent;

FIG. 9 is the view of FIG. 5 following expansion of the stent to anenlarged diameter;

FIG. 10 is a plan view of a first prior art stent as it would appear ifit were longitudinally split and laid out flat;

FIG. 11 is the view of FIG. 10 with the stent modified for support beamsto include parallel, spaced elements in accordance with the presentinvention;

FIG. 12 is a plan view of a second prior art stent as it would appear ifit were longitudinally split and laid out flat; and

FIG. 13 is the view of FIG. 12 with the stent modified for support beamsto include parallel, spaced elements in accordance with the presentinvention.

V. DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the several drawing figures in which identical elementsare numbered identically, a description of the preferred embodiment ofthe present invention will now be provided. Where several embodimentsare shown, common elements are similarly numbered and not separatelydescribed with the addition of apostrophes to distinguish theembodiments.

As will be more fully described, the present invention is directed to anovel support beam for an expandable stent. The support beam isapplicable to a wide variety of stent designs. In a preferredembodiment, the support beam will be used as a longitudinal segment in astent as described in the aforementioned U.S. patent application Ser.No. 09/049,486 filed Mar. 27, 1998, entitled “STENT” and naming Paul J.Thompson as sole inventor. Therefore, such a stent will now be describedwith reference to FIGS. 1 to 9. Subsequently, the use of the novel beamwill be described in use with other stent designs (i.e., those shown inU.S. Pat. No. 5,449,373 to Pinchasik et al. and U.S. Pat. No. 5,695,516to Fischell) to illustrate the broad range of applicability of the novelsupport beam to a wide range of other stent designs.

FIG. 1 illustrates a stent 10 having a rest length L_(r) and anun-deployed or reduced diameter D_(r). The stent 10 is of the designshown in the aforementioned U.S. patent application. The slot of thenovel beam construction, as will be described, is not shown in FIG. 1.

For ease of illustration, the stent 10 is shown flat in FIG. 2 whichillustrates a rest circumference C_(r) (C_(r)=πD_(r)). In FIG. 2,locations A, B, C, D and E are shown severed from their normallyintegrally formed locations A₁, B₁, C₁, D₁ and E₁. This permits thestent 10 to be shown as if it were severed at normally integrally formedlocations A-A₁, B-B₁, C-C₁, D-D₁ and E-E₁ and laid flat. FIG. 6 is anenlarged portion of the view of FIG. 2 to better illustrate a cellstructure as will be described.

The stent 10 is a reticulated, hollow tube. The stent 10 may be expandedfrom the rest diameter D_(r) (and corresponding rest circumferenceC_(r)) to an expanded or enlarged diameter. FIG. 3 is a view similar toFIG. 2 (i.e., illustrating the expanded stent 10 as it would appear iflongitudinally split and laid flat). Since FIG. 3 is a two-dimensionalrepresentation, the enlarged diameter is not shown. However, theenlarged circumference C_(e) is shown as well as a length L_(e)following expansion. The expanded diameter is equal to C_(e)/π.

As will be discussed length L_(e) is preferably not more than minimallysmaller (e.g., less than 10% smaller) than length L_(r). Ideally, L_(e)equals L_(r).

The material of the stent 10 defines a plurality of cells 12. The cells12 are bounded areas which are open (i.e., extend through the wallthickness of the stent 10). The stent 10 may be formed through anysuitable means including laser or chemical milling. In such processes, ahollow cylindrical tube is milled to remove material and form the opencells 12.

The cells 12 have a longitudinal or major axis X_(M)-X_(M) and atransverse or minor axis X_(m)-X_(m). In the embodiments of FIGS. 1-3,the major axis X_(M)-X_(M) is perpendicular to the longitudinalcylindrical axis X-X of the stent 10. In the embodiments of FIGS. 8 and9, the major axis X_(M)′-X_(M)′ is parallel to the longitudinalcylindrical axis X′-X′ of the stent 10′. The cell 12 is symmetricalabout axes X_(M)-X_(M) and X_(m)-X_(m).

The cell 12 is defined by portions of the tube material including firstand second longitudinal segments or support beams 14. The beams 14 eachhave a longitudinal axis X_(a)-X_(a) (shown in FIG. 6). The beams'longitudinal axes X_(a)-X_(a) are parallel to and positioned on oppositesides of the cell major axis X_(M)-X_(M).

Referring to FIG. 6, each of longitudinal beams 14 has an undulatingpattern to define a plurality of peaks 17, 21, 25 and valleys 19, 23.The peaks 17, 21, 25 are spaced outwardly from the longitudinal axesX_(a)-X_(a) and the valleys 19, 23 are spaced inwardly from thelongitudinal axes X_(a)-X_(a). As used in this context, “inward” and“outward” mean toward and away from, respectively, the cell's major axisX_(M)-X_(M).

Each of the peaks 17, 21, 25 and valleys 19, 23 is a generallysemi-circular arcuate segment. The peaks 17, 21, 25 and valleys 19, 23are joined by parallel and spaced-apart straight segments 16, 18, 20,22, 24 and 26 which extend perpendicular to the major axis X_(M)-X_(M).Linearly aligned straight end portions 16, 26 of opposing segments 14are joined at first and second longitudinal connection locations 27spaced apart on the major axis X_(M)-X_(M). First and second transverseconnection locations 28 are spaced apart on the minor axis X_(m)-X_(m).The first and second transverse connection locations 28 are positionedat the apices of the center peaks 21 of the longitudinal beams 14.

Slots 30 are formed through the complete thickness of each of the beams14. The slots 30 extend between first and second ends 31, 32. The firstends 31 are adjacent the longitudinal connection locations 27. Thesecond ends 32 are adjacent the transverse connection locations 28. Theslots 30 divide the beams 14 into first and second parallel elements 14₁, 14 ₂.

Except as will be described, the beams 14 have uniform cross-sectionaldimensions throughout their length as illustrated in FIG. 4. By way ofnon-limiting example, the width W and thickness T of the straight linesegments 16, 18, 20, 22, 24 and 26 are about 0.0065 inch (about 0.16 mm)and about 0.0057 inch (about 0.14 mm), respectively. The width Wincludes the widths (each of equal width) of the two elements 14 ₁, 14 ₂plus the width W_(S) of the slot 30. By way of a non-limiting example,the width W_(S) is in the range of 0.001 to 0.0025 inch. By way ofanother non-limiting example, the width W_(S) is less than 0.005 inch.

For reasons that will be described, the width W (FIG. 5) at the apicesof the peaks 17, 21, 25 and valleys 19, 23 is narrower than width W (inthe example given, narrow width W′ is about 0.055 inch or about 0.13mm). The width of the peaks 17, 21, 25 and valleys 19, 23 graduallyincreases from width W′ at the apices to width W at the straightsegments 16, 18, 20, 22, 24 and 26. At the longitudinal and transverseconnection locations 27, 28, the width W_(C) (shown in FIG. 2) ispreferably equal to or less than the common width W. Preferably, thewidth W_(S) of slot 30 remains constant throughout its length.

The combined lengths of segments 16-20 to the apex of peak 21 representa path length 50 from longitudinal connection location 27 to transverseconnection location 28. Similarly the combined lengths of the otherarcuate and straight segments 22-26 to the apex of peak 21 representidentical length path lengths 51 of identical geometry from longitudinalconnection locations 27 to transverse connection locations 28. Each ofthe path lengths 50, 51 is longer than a straight-line distance betweenthe transverse and longitudinal connection locations 27, 28. As will bedescribed, the straight-line distance between the transverse andlongitudinal connection locations 27, 28 increases as the diameter ofthe stent 10 is expanded. The path lengths 50, 51 are sized to be notless than the expanded straight-line distance.

The stent 10 includes a plurality of identical cells 12. Opposite edgesof the segments 14 define obliquely adjacent cells (such as cells 12 ₁,12 ₂ in FIG. 2). Cells 12 having major axes X_(M)-X_(M) collinear withthe major axis X_(M)-X_(M) of cell 12 are interconnected at thelongitudinal connection locations 27. Cells having minor axes collinearwith the minor axis X_(m)-X_(m) of cell 12 are interconnected at thetransverse connection locations 28.

As mentioned, the stent 10 in the reduced diameter of FIG. 1 is advancedto a site in a lumen. The stent 10 is then expanded at the site. Thestent 10 may be expanded through any conventional means. For example,the stent 10 in the reduced diameter may be placed on the balloon tip ofa catheter. At the site, the balloon is expanded to generate radialforces on the interior of the stent 10. The radial forces urge the stent10 to radially expand without appreciable longitudinal expansion orcontraction. Plastic deformation of the material of the stent 10 (e.g.,stainless steel) results in the stent 10 retaining the expanded shapefollowing subsequent deflation of the balloon. Alternatively, the stent10 may be formed of a super-elastic or shape memory material (such asnitinol—a well-known stent material which is an alloy of nickel andtitanium).

As the stent 10 expands, the path lengths 50, 51 straighten toaccommodate the expansion. During such change in geometry of the pathlengths 50, 51, each of the elements 14 ₁, 14 ₂ similarly changes ingeometry so that. At all times, the elements 14 ₁, 14 ₂ are mutuallyparallel and separated by spacing 30.

FIG. 3 illustrates the straightening of the path lengths 50, 51. In FIG.3, the stent 10 has been only partially expanded to an expanded diameterless than a maximum expanded diameter. At a maximum expanded size, thepath lengths 50, 51 are fully straight. Further expansion of the stent10 beyond the maximum expanded size would result in narrowing of theminor axis X_(m)-X_(m) (i.e., a narrowing of a separation between thetransverse connection locations and a resulting narrowing of the lengthL, of the stent) or would require stretching and thinning of the stentmaterial.

As shown in FIG. 3, during expansion of the stent 10, the straightsegments 16, 18, 20, 22, 24 and 26 are substantially unchanged. Thestraightening of the path lengths 50, 51 results in bending of thearcuate peaks 17, 21, 25 and valleys 19, 23. Since the width W′ of thepeaks 17, 21, 25 and valleys 19, 23 is less than the width W of thestraight segments 16, 18, 20, 22, 24 and 26, the arcuate peaks 17, 21,25 and valleys 19, 23 are less stiff than the straight segments 16, 18,20, 22, 24 and 26 and, therefore, more likely to deform duringexpansion.

As the geometry of the beams 14 changes during expansion, the geometryof the first and second elements 14 ₁, 14 ₂ similarly changes so thatthe elements 14 ₁, 14 ₂ remain in mutually parallel relation both beforeand after expansion. As used in this application, the term “mutuallyparallel” means the spacing 30 between the elements 14 ₁, 14 ₂ issubstantially constant throughout the length of the elements 14 ₁, 14 ₂.The elements 14 ₁, 14 ₂ and beam 14 may be curved or straight throughouttheir lengths.

As the stent 10 expands, the cells 12 assume a diamond shape shown inFIG. 3. Since the expansion forces are radial, the length of the majoraxis X_(M)-X_(M) (i.e., the distance between the longitudinal connectionlocations 27) increases. The length of the minor axis X_(m)-X_(m) (andhence the length of the stent 10) remains unchanged.

The stent highly flexible. To advance to a site, the axis X-X of thestent 10 must bend to navigate through a curved lumen. Further, forplacement at a curved site in a lumen, the stent 10 must be sufficientlyflexible to retain a curved shape following expansion and to bend as thelumen bends over time. The stent 10, as described above, achieves theseobjections.

When bending on its axis X-X, the stent 10 tends to axially compress onthe inside of the bend and axially expand on the outside of the bend.The present design permits such axial expansion and contraction. Thenovel cell geometry 12 results in an accordion-like structure which ishighly flexible before and after radial expansion. Further, the diamondshape of the cells 12 after radial expansion resists constricting forcesotherwise tending to collapse the stent 10.

The dual support structure of the elements separated by the slotsincreases flexibility without reducing resistance to compression forces.Further, during expansion and during flexing of the stent on its axis,the use of parallel, spaced elements 14 ₁, 14 ₂ results in lower stresslevels than would be experienced by a solid beam.

Numerous modifications are possible. For example the stent 10 may belined with either an inner or outer sleeve (such as polyester fabric orePTFE) for tissue growth. Also, the stent may be coated with radiopaquecoatings such as platinum, gold, tungsten or tantalum. In addition tomaterials previously discussed, the stent may be formed of any one of awide variety of previous known materials including, without limitation,MP35N, tantalum, platinum, gold, Elgiloy and Phynox.

While three cells 12 are shown in FIG. 2 longitudinally connectedsurrounding the circumference C_(r) of the stent, a different numbercould be so connected to vary the properties of the stent 10 as adesigner may elect. Likewise, while each column of cells 12 in FIG. 2 isshown as having three longitudinally connected cells 12, the number oflongitudinally connected cells 12 could vary to adjust the properties ofthe stent. Also, while each longitudinal segment 14 is shown as havingthree peaks 17, 21, 25 per longitudinal segment 14, the number of peakscould vary. FIG. 7 illustrates a stent 10″ with a cell 12″ having fivepeaks 117″, 17″, 21″, 25″ and 125″ per longitudinal segment 14″.Preferably, the longitudinal segment will have an odd number of peaks sothat the transverse connection points are at an apex of a center peak.In FIG. 7, no slot is shown in the beams 14″ for ease of illustration.

FIGS. 8 and 9 illustrate an alternative embodiment where the major axisX_(M)′-X_(M)′ of the cells 12′ are parallel with the cylindrical axisX′-X′ of the stent 10′. In FIG. 9, the expanded stent 10′ is shown at anear fully expanded state where the path lengths 50′, 51′ aresubstantially linear. In FIGS. 8 and 9, no slots are shown in the beams14′ for ease of illustration.

FIGS. 10 and 12 illustrate prior art stent designs. FIG. 10 is a stent10 a as shown in U.S. Pat. No. 5,449,373 to Pinchasik et al. and FIG. 12is a stent 10 b as shown in U.S. Pat. No. 5,695,516 to Fischell. Stent10 a is shown flat as if longitudinally split at locations Aa-Aa₁through Pa-Pa₁. Similarly, Stent 10 b is shown flat as if longitudinallysplit at locations Ab-Ab₁ through Eb-Eb₁.

Both of the designs of FIGS. 10 and 12 include solid structural beams 14a, 14 b. Beams 14 a are curved when the stent 10 a is in a reduceddiameter state. The beams 14 a cooperate to define cells 12 a. Thecurved beams 14 a straighten when the stent 10 a expands. The beams 14 bare straight and cooperate to define a butterfly-shaped cell 12 b. Uponexpansion, the beams 14 b remain straight but pivot for the cell 12 b toassume a hexagon shape upon expansion.

The dual support structure aspect of the present invention is applicableto prior art stents such as those shown in FIGS. 10 and 12. FIGS. 11 and13 show the prior art stents of FIGS. 10 and 11, respectively, modifiedaccording to the dual support structure aspect of the present invention.Specifically, beams 14 a′, 14 b′ are provided with slots 30 a, 30 b todivide the beams into parallel, spaced first and second elements 14 a₁′, 14 a ₂′ and 14 b ₁′, 14 b ₂′ having the benefits previouslydescribed.

From the foregoing, the present invention has been shown in a preferredembodiment. Modifications and equivalents are intended to be includedwithin the scope of the appended claims.

1. An intraluminal stent comprising: a reticulated tube having anun-deployed diameter and expandable to an enlarged diameter, said tubehaving a stent axis; said tube including a structural beam extendingbetween first and second ends; said structural beam changing from afirst geometry to a second geometry when said tube changes from saidun-deployed diameter to said enlarged diameter; said structural beamincluding first and second longitudinal elements each extending at leastpartially between said first and second ends and with a spacing betweenthe first and second elements; each of said first and second elementschanging from said first geometry to said second geometry when said tubechanges from said un-deployed diameter to said enlarged diameter forsaid spacing to remain substantially unchanged as said tube changes fromsaid un-deployed diameter to said enlarged diameter. 2-10. (canceled)